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high occlusion in the final prosthesis and thus minimizes or eliminates the time required for occlusal adjustments. An added side benefit is that, rather than having to pour up the opposing alginate impression in the dental office, this alginate substitute VPS can be shipped along with the impression of the prepared teeth and bite registration to the dental laboratory. Thus, the time and cost incurred for pouring up the impression in the dental office is removed. This opposing cast fabrication becomes part of the laboratory fee, which more than compensates for the increased cost of taking the impression with an alginate substitute. DUAL-ARCH IMPRESSIONS It should now be abundantly clear why properly fabricated dual-arch impressions “produce mounted casts with significantly more accurate maximal intercuspal relationships than mounted casts from full-arch impressions.” 4 The dualarch impression, as an all-in-one technique, is faster, uses less impression material, and is easier for the clinician and the patient. 35 However, to be successful with the dual-arch impression tray, there are strict parameters for its use. The rear bar (connector) of the dual-arch tray must comfortably pass through the interocclusal retromolar area with no interference to proper closure. With the dual-arch technique, the prepared teeth should be bordered by intact teeth with centric stops (Fig. 14). 36 Single-tooth preparations that fit this criteria are indicated, but multiple tooth preparations may be problematic. 1,37 Because the articulators used for mounting dual-arch impressions are simple hinges (usually flexible plastic), the patient must have a cuspid rise (canine guidance) disclusion, not group function. Therefore, the canine tooth must be registered in the impression. 5 This is facilitated by full-quadrant metal trays (such as the QUAD-TRAY ® XL [CLINICIAN’S CHOICE]) (Fig. 15). Plastic trays can flex, resulting in a distorted impression. Flexure occurs due to the hydraulic pressures of the impression material, tray side walls impinging on hard tissue (Figs. 16, 17), axial roll or vertical flex of the plastic side walls, the action of swallowing by the patient during impression-taking, and elastic rebound upon removal of the impression. 38–40 The dual-arch tray must be rigid, 41 making metal trays the tray material of choice. In addition, a complementary rigid (stiff) impression material will increase the chance of overall success with this technique (Fig. 18). 36,38 The ADA, in its review of elastomeric impression materials, recommended an impression material with a strain in compression (stiffness) of less than 2 percent 42 be used for the dual-arch impression technique. Nine of the 10 heavy body impression materials tested in this review did not meet this criterion; only Correct Plus ® (Pentron Clinical Technologies) was found to have a strain in compression of 1.5 percent. Another VPS material on the market, AFFINITY Inflex, is also especially well suited for the dual-arch impression technique and has a strain in compression of 1.3 percent (Fig. 19). CONCLUSION For predictability in mounting or articulating models, it is prudent to use materials of matching accuracy so that the components work in harmony. To ensure clinical success, Figure 14: In following the correct dual-arch impression technique protocol, the prepared tooth should have teeth with centric stops on either side. Figure 15: A full-quadrant metal tray (such as QUAD-TRAY XL) picks up the cuspid in the impression so that the cuspid (canine) rise occlusion can be replicated in the laboratory. 52 www.chairsidemagazine.com
It should now be abundantly clear why properly fabricated dual-arch impressions “produce mounted casts with significantly more accurate maximal intercuspal relationships than mounted casts from full-arch impressions.” Figure 16: Preparation view of a dual-arch impression taken with a flexible plastic tray. This impression was distorted due to hard-tissue impingement. Figure 17: The opposing side must also be visually checked. Tissue contact seen here can cause flex or axial roll. Figure 18: A rigid metal tray with a complementary rigid techniquedesigned impression material will yield the most accurate models and final prosthesis. Figure 19: A dual-arch impression using a technique-designed stiff VPS impression material (AFFINITY Inflex) Optimizing Occlusal Results for Crown & Bridge Prostheses53
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Chairside® A Publication of Glidew
Page 4 and 5: Contents 38 CEREC ® Connect: A Wel
Page 6 and 7: Letters to the Editor Dear Dr. DiTo
Page 8 and 9: Contributors Michael C. DiTolla, DD
Page 10 and 11: Numbers by the An elephant’s mola
Page 12 and 13: Dr. DiTolla’s CLINICAL TIPS PRODU
Page 14: Dr. DiTolla’s CLINICAL TIPS PRODU
Page 17 and 18: Figure 1: Tooth #9 is going to be p
Page 19 and 20: Figure 7: Crowns often look fake in
Page 21 and 22: Figure 15: The prep is essentially
Page 23: Depth cuts ensure that we get enoug
Page 27 and 28: Interview with Stephen Thorne - INT
Page 29 and 30: ST: No, it was definitely the forme
Page 31 and 32: can share a blog. There are many ti
Page 33 and 34: After those steps, Owner Dentists t
Page 35 and 36: dental schools, and I thought that
Page 37 and 38: all the way through retirement. And
Page 40 and 41: CEREC ® Connect: A Welcomed Upgrad
Page 42 and 43: Many CEREC ® dentists find making
Page 44 and 45: Figure 1 Figure 2 CEREC Connect Pro
Page 46: Figure 5 Figure 6 Conclusion CEREC
Page 50 and 51: working stone model of the single p
Page 52 and 53: detailed occlusal anatomy picked up
Page 56: use a high-flow, stiff (no bounce)
Page 60 and 61: most overlooked esthetic zone 3,4 (
Page 62 and 63: and floss. The facial and lingual p
Page 64: metal designs like the Wynne Hybrid
Page 67: The Chairside® PHOT Hunt Eleven ye
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